Ring-jet sensors (also called reflex eyes) as signal generators in devices of this kind have the advantage that a heavy incidence of dirt, sources of noise, the risk of explosion, complete darkness, transparency or magnetic properties of the objects have no disturbing influence on their ability to function. They are also capable of emitting useful counting signals without a direct contact taking place between the ring-jet sensor and the object. Apart from the nozzle-like outlet of the ring-jet sensors, said sensors have, in the known devices of the type mentioned at the outset, two connections, namely one (often designated P) for the air supplied and one (often designated A) as signal connection for the pressure signal to be evaluated.
The requirement up to now that ring-jet sensors be provided with two connecting lines is a disadvantage which the invention aims to eliminate
Accordingly, it is an object of the invention to provide a ring-jet sensor in a device using a single connecting line to the sensor.